feat(ui): persist selectedProfileId across sessions

Wrap useUIStore in zustand/middleware's persist under the key
voicebox-ui. partialize only selectedProfileId so volatile UI state
(dialog open flags, form drafts, engine/voice pickers, sidebar) stays
in-memory as before — but reopening the app no longer loses whichever
profile the user was last working with.

Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>

app/src/stores/uiStore.ts

@@ -1,4 +1,5 @@
 import { create } from 'zustand';
+import { persist } from 'zustand/middleware';
 
 // Draft state for the create voice profile form
 export interface ProfileFormDraft {
@@ -49,7 +50,9 @@ interface UIStore {
   setTheme: (theme: 'light' | 'dark') => void;
 }
 
-export const useUIStore = create<UIStore>((set) => ({
+export const useUIStore = create<UIStore>()(
+  persist(
+    (set) => ({
       sidebarOpen: true,
       setSidebarOpen: (open) => set({ sidebarOpen: open }),
 
@@ -78,4 +81,10 @@ export const useUIStore = create<UIStore>((set) => ({
         set({ theme });
         document.documentElement.classList.toggle('dark', theme === 'dark');
       },
-}));
+    }),
+    {
+      name: 'voicebox-ui',
+      partialize: (state) => ({ selectedProfileId: state.selectedProfileId }),
+    },
+  ),
+);